Electromagnet



Jan. 12, 1960 J. D. LEITCH 2,921,242

ELECTROMAGNET Filed Oct. 29, 1956 2 Sheets-Sheet 1 INVENTOR. JOHN D. LEITCH BY 2444444; (Emmi? J. D. LEITCH ELECTROMAGNET Jan. 12, 1960 2 Sheets-Sheet 2 Filed Oct. 29. 1956 INVENTOR. JOHN I7. LEITCH 1/ Qua.

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United States Patent ce ELECTROMAGNET John D. Leitch, Grosse Pointe Park, Mich., assignor to Square D Company, Detroit, Mich., a corporation of Michigan Application October 29, 1956, Serial No. 618,782

6 Claims. (Cl. 317-158) the boss serving as an inner pole piece. An annular magnetizing winding is mounted in the channel co-axial with respect to the inner and outer pole pieces, and the channel opening is closed by an annular sealing plate tightly fastened, as by screws or welding, to both the inner and the outer pole pieces and forming with the magnet case a complete enclosure for the winding. The winding, which comprises a plurality of turns of wire, is either wound and taped so as to be-self-supporting or is wound upon a tubular core which is open at both ends and fits around the central pole piece so as to leave the outer face of the central pole piece exposed. A sealing plate, often annular in form, is connected to the core and also to the outer pole piece by welding or by a very large number of screws in each instance.

A common prior practice is to impregnate the completed winding of such magnets with a liquid material which later solidifies to form an insulating coating over what would otherwise be relatively exposed portions of the winding. The winding and its core, if there be one, are then positioned within the annular channel and are accommodated therein with considerable clearance. The spaces between the winding and the walls of the case are either filled with the same material used to cover the winding or with a material compatible thereto. Recently, windings for magnets which are to be subjected to severe 'service conditions have been, before insertion into the case, completely encapsulated into a toroidal container formed of sheet metal. After the winding is placed in "the container, the container is filled with the insulating material.

Heretofore, the central opening of the container which receives the central pole piece extends completely through the container and the outer face of the central pole piece is exposed. The outer annular wall of the container serves as the sealing plate for the magnet and extends a short distance radially inwardly from the inner cylindrical wall of the container to define an inner annular flange and extends a short distance radially outwardly from the outer cylindrical wall of the container to define an outer an have several disadvantages. For example, because of 2,921,242 Patented Jan. 12, 1960 the complete encapsulation of the coil and consequent entrapment of air, it is diflicult to insure that all of the space in the coil container is filled with the liquid insulating material; sometimes all of the liquid does not turn to a solid and whether it has or has not cannot be easily determined; the container is difficult to make; and the welding or other fastening means required between the container and the case, particularly at the outer pole piece, is expensive and renders removal of the coil unit from the case dilficult.

It is an object of this invention to provide an electromagnet that does not have the foregoing disadvantages.

A specific electromagnet embodying this invention is one having a coil container comprising a continuous, disc-like circular base plate formed from sheet metal, and inner and outer cylindrical wall portions rigid therewith. An edge portion of each side wall is bent over to define an annular flange for spot-welding the wall to the base. The outer side wall is spaced inwardly from the peripheral edge of the base plate to provide an outerannular flange. When assembled on the base plate, theside walls are concentric and define an annular coil-receiving channel. A multi-turn, annular coil is received in the channel of the container and the channel is then filled with a suitable insulating material that hardens to form a solid mass, the air or other gases escaping through the open side of the channel. The coil leads extends outwardly from the surface of the hardened insulating material, and the material itself serves as a closure for what would otherwise be an open end of the coil container. The coil container with the coil embedded in the insulating material, is received in the annular space in the magnet case or frame member with the base plate outermost, the clearances between the pole pieces and the respective side walls of the container being very small so that but slight radial movement between the coil unit and case is possible. The leads extend through respective openings in the rear wall of the case. The base plate completely overlies the outer face of the central or inner pole piece and the outer annular flange of the base plate fits snugly in an annular shouldered recess formed along the inner peripheral margin of the outer face of the outer pole piece. Because of the rigidity of the coil container resulting from the use of a continuous base plate and because of the snug fit between the coil unit and the case, the coil unit is securely held in position solely by detachable fastening means such as screws passing through the central area of the base plate and threaded into the central pole piece.

Other objects of this invention are to provide an improved electromagnet, to provide an electromagnet having a metal coil container that can be entirely assembled by spot welding, to provide an electromagnet having a coil container that can be easily filled with liquid insulating material without gas entrapment, to provide an improved electromagnet in which one wall of the coil container constitutes a sealing plate for the coil space, and to provide an electromagnet in which the coil container is so rigid that it can be secured in position by fastening means solely at the central pole piece.

Other objects and advantages will become apparent from the following description wherein reference is made to the drawings, in which:

Fig. l is a side elevation of an electromagnet in accordance with this invention shown with an associated armature.

Fig. 2 is a sectional view taken along the line 22 of Fig. 1.

Fig. 3 is a sectional view taken along the lines 33 of Fig. 2, and

Fig. 4 is a perspective view of the coil container of the electromagnet of Figs. 1, 2 and 3.

An electromagnet illustrative of this invention as shown in the drawings comprises a hollow, bowl-like case of cast steel having a pair of spaced lower leg portions 11 supported on a shaft 12 which also pivotally carries a disc-shaped armature 14 biased away from the case 10 by a helical spring 15 disposed between upwardly projecting brackets 16 and 17 on the case it) and armature 1-4, respectively. An operating linkage (not shown can be attached to a projection 18 of the armature 14 for operating a brake orthe like. The armature shown in Fig. 1 forms no part of the present invention and is merely illustrative of one possible application for the magnet. t

The magnet case 10, as shown most clearly in Fig. 3, comprises a body portion 24) having an outer peripheral flange 21 and a central boss 22 defining an annular winding space 23 therebetween closed at the rear by anannular wall portion 24. The outer peripheral flange 21 constitutes an outer pole piece of the magnet and the central boss 22 constitutes an inner pole piece. A coil unit 25 to be described is received in the Winding space 23. Circumferentially spaced openings 26 and 27 in the wall portion 24 permit leads 28 and 29 from the coil unit'25 to extend outwardly from the rear of the case 10 for connection to a suitable source of power.

The coil unit 25 comprises a suitably insulated multiturn winding 30 received in a sheet metal container 31 open at the one end and filled with a thermal-plastic or thermal-setting insulating material 32. The container 31 has a continuous circular base plate 36 of sheet metal, preferably steel, and inner and outer cylindrical wall portions 38 and 39 also preferably formed from sheet steel and shaped into cylindrical form. As shown best in Fig. 3, edge portions of the walls 38 and 39 are bent over to define respective annular flanges 4t and 41 which are spot-welded to the base plate 36. Preferably, the flange 40 is turned outwardly and the flange 41 is turned inwardly. When assembled on the base plate 36, the walls 38 and 39 are concentric and define an annular coil receiving chamber 42. V V

The coil unit 25 is received very snugly in the winding space 23 with just sufficient clearance between the inner wall 38 and the pole piece 22 and between the outer wall 39 and the pole piece 21 to permit telescoping, without any substantial radial movement, of the coil container 31 into the caseLltl by its 'own weight when the container is lowered into the open end of. the inverted case. To this end, the opposite end portions of the sheet defining the wall 38 overlap each other, as shown at 44, so as to present a smooth innermost peripheral surface of uniform diameter and the end portions of the sheet defining the wall 39 overlap each other, as shown at 45, so as to present a smooth outermost peripheral surface of uniform diameter. Preferably the overlapped end portions of the sheet defining the wall 38 and the overlapped end portions of the sheet defining the wall 39 are spot-welded together. Thus the container 31 is substantially coextensive radially with the winding space 23.

When the Winding St) is placed'in the annular chamber 42, it is held in spaced relation with respect to the base plate 36 by suitable insulating spacers 47 and the chamber 42 is filled with the insulating material 32. Any suitable insulating material 32 can be used, but preferably it comprises a slate-filled, epoxy resin of the pourable type which, after mixing with an amineactivator, solidifies at room temperature to a dense, hard, heat resisting, and tough mass having good adhesive properties. The coil leads 28 and 29 extend outwardly from the surface of the material 32 and the material i self when hardened serves as a closure for the inner end of the container 31.

Thecoil unit 25 is received in the annular space 23 in the magnet case 10 with the leads 28 and 29 extending through the respective openings 26 and 27, and with the central portion of, the base plate 36 completely overlying the outer face of the inner pole piece 22. The coil unit 25 is secured to'the case 10 by fastening means consisting of fastening elements such as flat-head screws 48 passing through respective openings 49 in the central portion of the base plate 36 and threaded into complementary holes tapped in the pole piece 22 of the case 10. It should be noted that the leads 28 and 29 must be positioned accurately in proper angular relation with respect to the openings 49 so that they were properly aligned with the openings 26 and 27 when the openings 49 are aligned with their associated tapped holes in the I pole piece 22. I

An outer annular flange portion of the base plate 36 fits snugly in a shouldered recess 52 formed along the inner edge of the outer extremity of the pole piece 21. Because the inner surface of the base plate 36 is coplanar with the face of the inner pole piece 22 and because the baseplate 36 thus has an annular portion juxtaposed in face to face relation to, and coextensive with, the entire outer annular marginal portion of' the face of said inner pole piece 22, the coil unit 25 is very rigid, and no fastening means along the outer periphery of the base plate is required. The screws 43 secure the coil unit 25 to the magnet case 10 at these mutually coextensive annular portions.

In the illustrative example, not only the annular portion but the inner surface of the base plate 36, over an area coextensive with the face of the inner pole piece, is juxtaposed against the said face of the inner pole piece. 7

Although the base plate 36 is made of steel and bridges the pole pieces 21 and 22, its thinness prevents it from shunting sufficient flux to reduce materially the working flux.

While a certain preferred embodiment of the invention has been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

t Iclaim:

1. An electromagnet comprising a magnetic case having a body portion, concentrically arranged inner and outer pole pieces extending outwardly in the same direction from the body portion and defining therewith an annular winding space open at one end and closed at theother end, the inner pole piece having a flat outer face, an annular coil container fitting in, and substantially coextensive. radially with, said winding space, said container having a metal bottom wall, an outer cylindrical metal side wall, and an inner cylindrical metal side wall coaxial with said outer side wall andspaced radially inwardly therefrom, said inner and outer walls being rigidly secured to said bottom wall, a coil fitting in said container between said inner and outer walls, said bottom wall having portions juxtaposed in face to face relation against circumferentially spaced portions of the outer face of said inner pole piece, respectively, fastening means consisting. of fastening elements which extend through said juxtaposed portions and detachably secure said bottom wall to said inner pole piece in firm juxtaposition with the outer face of said inner pole piece, said bottom wall extending radially outwardly beyond the inner pole piece at least to the inner periphery of the outer pole piece, and said bottom wall being secured to said case solely by said elements.

2. An electromagnet comprising a' magnetic case having a body portion, concentrically arranged inner and outer pole pieces extending outwardly in the same direction from the body portion and defining therewith an annular winding space open at one end and closed at the other end, the inner pole piece having a flat outer face,

' an annular coil container fitting in, and substantially coextensive with, said winding space, said container having a metal bottom wall, an outer cylindrical metal side wall,

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, and an inner cylindrical metal side wall coaxial with said outer side wall and spaced radially inwardly therefrom, said inner and outer walls being rigidly secured to said bottom Wall, a coil fitting in said container between said inner and outer walls, said bottom wall having an annular portion juxtaposed in face to face relation to, and coextensive with, the entire outer annular marginal portion of the outer face of said inner pole piece, fastening means consisting of fastening elements which extend through said coextensive portions of the bottom wall and detachably secure said bottom wall to said inner pole piece in firm juxtaposition with said outer marginal portion of the outer face of said inner pole piece, said bottom Wall extending radially outwardly beyond the inner pole piece at least to the inner periphery of the outer pole piece, and said bottom wall being secured to said case solely by said elements. 1

3. An electromagnet comprising a magnetic case having a body portion, concentrically arranged inner and outer pole pieces extending outwardly in the same direction from the body portion and defining therewith an annular winding space open at one end and closed at the other end, the inner pole piece having a flat outer face, an annular coil container fitting in, and substantially coextensive with, said winding space, said container having a metal bottom wall, an outer cylindrical metal side wall, and an inner cylindrical metal side wall coaxial with said outer side wall and spaced radially inwardly therefrom, said inner and outer walls being rigidly secured to said bottom wall, a coil fitting in said container between said inner and outer walls, said bottom wall having an annular portion juxtaposed in face to face relation to, and coextensive with, the entire outer annular marginal portion of the outer face of said inner pole piece, fastening means consisting of fastening elements which extend through said coextensive portions of the bottom wall and detachably secure said bottom wall to said inner pole piece in firm juxtaposition with said outer marginal portion of the outer face of said inner pole piece, said bottom wall having an outer marginal portion juxtaposed against a portion of the outer face of the outer pole piece, and said bottom wall being secured to said case solely by said elements.

4. An electromagnet comprising a magnetic case having a body portion, concentrically arranged inner and outer pole pieces extending outwardly in the same direction from the body portion and defining therewith an annular winding space open at one end and closed at the other end, the inner pole piece having a flat outer face, an annular coil container fitting in, and substantially coextensive radially with, said winding space, said container having a metal bottom wall, an outer cylindrical metal side wall, and an inner cylindrical metal side wall coaxial with said outer side wall and spaced radially inwardly therefrom, said inner and outer walls being rigidly secured to said bottom wall, the end of the container opposite from said bottom wall being open, a coil fitting in said container between said inner and outer walls, said bottom wall having portions juxtaposed in face to face relation against circumferentially spaced portions of the outer face of said inner pole piece, respectively, fastening means consisting of fastening elements which extend through said juxtaposed portions and detachably secure said bottom wall to said inner pole piece in firm juxta- 6 position with the outer face of said inner pole piece, said bottom Wall extending radially outwardly beyond the inner pole piece at least to the inner periphery of the outer pole piece, and said bottom wall being secured to said case solely by said elements.

5. An electromagnet comprising a magnetic case having a body portion, concentrically arranged inner and outer pole pieces extending outwardly in the same direction from the body portion and defining therewith an annular winding space open at one end and closed at the other end, the inner pole piece having a flat outer face, an annular coil container fitting in, and substantially coextensive radially with, said winding space, said container having a metal bottom Wall, an outer cylindrical metal side wall, and an inner cylindrical metal side wall coaxial with said outer side wall and spaced radially inwardly therefrom, said inner and outer walls being rigidly secured to said bottom Wall, a coil fitting in said container between said inner and outer walls, said bottom wall having a central portion coextensive radially with, and completely overlying, the outer face of said inner pole piece, fastening means consisting of fastening elements which extend through said central portion of the bottom wall and detachably secure said bottom wall to said inner pole piece in firm juxtaposition with the outer face of said inner pole piece, said bottom wall extending radially outwardly beyond the inner pole piece at least to the inner periphery of the outer pole piece, and said bottom wall being secured to said case solely by said elements.

6. An electromagnet comprising a magnetic flux conductive metal case having a thick body portion and concentrically arranged thick inner and outer pole portions integrally joined with the body portion and extending axially in the same direction therefrom and defining therewith an annular Winding space open at one end and closed at the other end, an annular coil container fitted in and substantially coextensive radially with said winding space, said container having a thin sheet metal bottom wall and concentrically arranged inner and outer thin sheet metal side walls extending axially in the same direction therefrom, each of said side walls having a generally radially extending flange on one end thereof, said flanges extending radially towards each other and being rigidly secured to said bottom Wall, an energizable flux producing coil in said container between said inner and outer walls and between said body portion and said bottom wall, fastening means detachably securing said bottom wall to said inner pole piece, and said bottom Wall extending radially outwardly beyond the outer wall at least to the outer pole portion of said case, whereby said case and said container completely enclose said coil.

References Cited in the file of this patent UNITED STATES PATENTS 1,212,555 Pragst Ian. 16, 1917 1,451,525 Bouton Apr. 10, 1923 1,511,229 McKee Oct. 14, 1924 1,750,149 Zamboni Mar. 11, 1930 2,030,648 Meissner Feb. 11, 1936 2,464,568 Flynn Mar. 15, 1949 2,560,926 Brownell July 17, 1951 

